This invention relates to a cooling system for an internal-combustion engine of a motor vehicle comprising a radiator and a thermostatic valve by means of which the temperature of the coolant can be controlled in a warm-up operation, a mixed operation and a radiator operation, the thermostatic valve containing an expansion element which can be electrically heated for reducing the coolant temperature.
In this case, the thermostatic valve controls the flow of the coolant between the internal-combustion engine and the radiator in such a manner that, during the warm-up operation, the coolant coming from the internal-combustion engine flows essentially while by-passing the radiator through a short circuit back to the internal-combustion engine, in that, during the mixed operation, the coolant coming from the internal-combustion engine flows partially through the radiator and partially through the short circuit back to the internal-combustion engine, and in that, during the radiator operation, the coolant coming from the internal-combustion engine flows essentially through the radiator back to the internal-combustion engine.
The electric heating of the expansion element is used for enlarging the opening cross-section toward the radiator in comparison to an opening cross-section caused by the temperature of the coolant in the area of the thermostatic valve.
A cooling system of the above-noted general type is known, for example, from German Patent Document DE 30 18 682 A1. In the case of this known cooling system, an electric heating resistor, to which electric energy can be fed through a stationarily held working piston, is arranged in an expansion element of a thermostatic valve. The supply of the electric energy takes place via a control device in order to be able to maintain the coolant temperature controlled by the thermostatic valve constant better than in the case of a normal thermostatic valve. For this purpose, the actual coolant temperature is measured and is compared with a given upper and with a given lower temperature value. When the upper temperature value is reached, the heating resistor is supplied with electric energy so that the thermostatic valve opens up farther in order to reach an increased cooling capacity and therefore a lowering of the actual coolant temperature. If the actual coolant temperature then falls below the lower temperature value, the supply of electric energy to the heating resistor is interrupted so that the expansion element is cooled by the colder coolant. As a result, the valve cross-section is reduced again so that the actual coolant temperature rises again. These control steps are constantly repeated in order to maintain a coolant temperature in the range of, for example, 95.degree. C. as constant as possible.
From German Patent Document DE 37 05 232 A1, a temperature control device is known in the case of which, instead of a conventional thermostatic valve with an expansion element, a valve is provided which can be controlled by means of a motor operator. In the case of this known temperature control device, for adjusting the valve, the motor operator is controlled as a function of a sensor which measures the coolant temperature in a pipe connected with the internal-combustion engine. In addition, the sensor is provided with a heating device. The heating device can be switched on and off as a function of characteristic-diagram quantities of the internal-combustion engine. Therefore, in the case of this known temperature control device, by heating the sensor, a higher than actual coolant temperature may be simulated in order to achieve an intensified cooling of the coolant. A temperature control device of this type requires high constructional expenditures and is therefore cost-intensive.
In German Patent Application P 43 24 178, which has not yet been published, a cooling system is also described for an internal-combustion engine of the initially mentioned type in the case of which the expansion element is designed such that the coolant temperature is adjusted to an upper limit temperature without any heating of the expansion element in the warm-up operation and/or in the mixed operation. In the case of this cooling system, a control unit is provided which, as a function of detected operational and/or environmental quantities of the internal-combustion engine, as required, releases the heating of the expansion element in order to shift the operating method of the cooling system from the warm-up operation or from the mixed operation of the upper operating limit temperature toward the mixed operation or cooling operation of a coolant temperature which is lower in comparison to the upper operating limit temperature. Since, in the case of this cooling system, the control of the expansion element of the thermostatic valve takes place as a function of detected operational and/or environmental quantities of the internal-combustion engine, an electronic control unit is required for controlling the heating of the expansion element in which the detected operational and/or environmental quantities of the internal-combustion engine are processed in a suitable manner and are used for controlling the heating of the expansion element.
It is an object of the invention to further develop a cooling system of the initially mentioned type in a manner that is as simple as possible such that, as a result, the operation of the internal-combustion engine can be optimized with respect to the fuel consumption and the exhaust gas values without any reduction of the power of the internal-combustion engine in the case of an increased power requirement.
This object is achieved by providing a cooling system for an internal-combustion engine of a motor vehicle comprising a radiator and a thermostatic valve by means of which the temperature of the coolant can be controlled in a warm-up operation, a mixed operation and a radiator operation, the thermostatic valve containing an expansion element which can be electrically heated for reducing the coolant temperature,
wherein, as a result of the design of the expansion element, the coolant temperature is controlled without any heating of the expansion element in the mixed operation to an upper operating limit temperature, and PA1 wherein a temperature switch is provided which, as a function of the coolant temperature detected at the or near the radiator outlet, releases the heating of the expansion element as required in order to shift the method of operation of the cooling system toward the radiator operation.
As a result of the design of the expansion element, the coolant temperature is controlled without any heating of the expansion element in the mixed operation to an upper operating limit temperature and a temperature switch is provided which, as a function of the coolant temperature detected at the or near the radiator outlet, releases the heating of the expansion element as required in order to shift the method of operation of the cooling system toward the radiator operation.
The upper operating limit temperature is preferably equal to the operating temperature of the internal-combustion engine which is most favorable with respect to consumption and is slightly lower than the maximally permissible operating temperature of the internal-combustion engine. Preferably, the upper operating limit temperature is above 100.degree. C., particularly at approximately 105.degree. C. The maximally permissible operating temperature is the highest possible temperature at which the internal-combustion engine can be operated in the normal operation for an extended period of time without any disturbances. As a result, even if the electric heating of the expansion element fails, damage to the internal-combustion engine is avoided. Normally, the maximally permissible operating temperature is between 105.degree. C. and 120.degree. C.
If the expansion element is not heated electrically, an opening cross-section toward the radiator occurs exclusively as a function of the coolant temperature of the internal-combustion engine. This opening cross-section causes an adjusting of the coolant temperature to the defined upper operating limit temperature. In this case, the expansion element, for example, by selecting a corresponding temperature-dependent material and a suitable constructive development, is designed such that, at the defined upper operating limit temperature, the opening cross-section of the radiator is not yet maximal; that is, no pure radiator operation is achieved. Thus, by means of an additional heating of the expansion element, a further enlargement of the opening cross-section is possible and therefore a shifting in the direction of the radiator operation.
In a supplementary manner, it should be pointed out that the opening cross-section toward the radiator and the opening cross-section toward the short circuit by-passing the radiator are changed in opposite directions.
By means of the cooling system according to the invention, in the normal operation, that is, not when the power requirement is increased, as, for example, in the full-load operation of the internal-combustion engine or during uphill driving of the motor vehicle driven by the internal-combustion engine, an operating temperature of the internal-combustion engine is reached which is as high as possible. In this case, for example, as a result of lower friction, the power consumption of the internal-combustion engine is lower, whereby the fuel consumption can be lowered and the exhaust gas composition can be improved. However, in order to permit, when the operating condition of the internal-combustion engine requires a lower coolant temperature level because of an increased power demand, a rapid switch-over to this coolant temperature level, a temperature switch is provided according to the invention which, as a function of the coolant temperature detected at the or near the radiator outlet, supplies electric energy to the heatable expansion element in such a manner that an increased cooling output is achieved by means of the further opening of the thermostatic valve and thus an increased coolant temperature is achieved in a rapid manner. Excessive coolant or internal-combustion engine temperatures in the case of an increased power requirement, would lead to a reduced volumetric efficiency and thus to a reduced power of the internal-combustion engine.
The advantage of the cooling system according to the invention in comparison to the cooling system in the not yet published German Patent Application P 43 24 178 is the fact that, as a function of different power requirements with respect to the internal-combustion engine, different coolant temperature levels can be achieved by means of a simple temperature switch while eliminating an electronic control unit which requires high technical expenditures and costs. Thus, the cooling system according to the invention is particularly suitable for an internal-combustion engine for motor vehicles of the lower price range. A further advantages of the cooling system according to the invention is the fact that the high-expenditures and cost-intensive detection of operational and environmental quantities of the internal-combustion engine will not be necessary.
The heating of the expansion element can be switched off again after a predetermined time, for example, in a time-controlled manner.
However, in the case of an advantageous further development of the invention, a two-position switch is provided as a temperature switch whose upper switching point is in the range of from 55.degree. C. to 75.degree. C., preferably at 65.degree. C. and whose lower switching point is minimally 5.degree. C. and maximally 50.degree. C. below the upper switching point. In this further development of the invention, the heating device of the expansion element is switched off again when the coolant temperature detected at the or near the radiator outlet falls below the lower switching point of the two-position switch.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.